Ion implantation is a process by which dopants or impurities are introduced into a substrate via bombardment. In semiconductor manufacturing, the dopants are introduced to alter electrical, optical, or mechanical property. For example, dopants may be introduced into an intrinsic semiconductor substrate to alter the type and level of conductivity of the substrate. In manufacturing an integrated circuit (IC), a precise doping profile is often important for proper IC performance. To achieve a desired doping profile, one or more dopants may be implanted in the form of ions in various doses and various energy levels.
Referring to FIG. 1, there is shown a conventional ion implantation system 100. As illustrated in the figure, the ion implantation system 100 may comprise an ion source and a complex series of beam-line components through which an ion beam 10 passes. The ion source may comprise an ion source chamber 102 where desired ions are generated. The ion source may also comprise a power source 101 and an extraction electrode assembly 104 disposed near the ion source chamber 102. As illustrated in the figure, the extraction electrode assembly 104 may include a suppression electrode 104a and a ground electrode 104b. Each of the ion source chamber 102, the suppression electrode 104a, and the ground electrode 104b may include an aperture: the ion source chamber 102 may include an extraction aperture (not shown), the suppression electrode may include a suppression electrode aperture (not shown), and a ground electrode may include a ground electrode aperture (not shown). The apertures may be in communication with one another so as to allow the ions generated in the ion source chamber 102 may pass through, toward the beam-line components. Hereinafter, the suppression electrode aperture and the ground electrode aperture may collectively be referred as an extraction electrode aperture assembly.
The beam-line components, meanwhile, may include, for example, a mass analyzer 106, a first acceleration or deceleration (A1 or D1) stage 108, a collimator 110, and a second acceleration or deceleration (A2 or D2) stage 112. Much like a series of optical lenses that manipulate a light beam, the beam-line components can filter, focus, and manipulate ions or ion beam 10 having desired species, shape, energy, and other qualities. The ion beam 10 that passes through the beam-line components may be directed toward a substrate 114 that is mounted on a platen 116 or clamp. The substrate 114 may be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat.” It should be appreciated by those skilled in the art that the entire path traversed by the ion beam 10 is typically evacuated during ion implantation.
The ion source is an important component of the ion implanter system 100. The ion source is required to generate a stable, well-defined ion beam 10 for a variety of different ion species and extraction voltages. It is therefore desirable to operate the ion source for extended periods of time without the need for maintenance or repair. The lifetime of the ion source or mean time between failures (MTBF) is one performance criteria of the ion source and an important metric for the performance of an ion implanter system 100.
One cause of ion source failure is accumulation of materials on the inner wall of the ion source chamber 102, the suppression electrode and the ground electrode. In addition, the materials may accumulate on the apertures. If formed on the inner wall of the ion source chamber 102, the materials may reduce the rate by which ions are generated and reduce the beam current.
Moreover, the ions generated and emitted from an ion source under such a condition may be less than optimal. The ions 10 may be unstable and may cause ion beam current drifts and, in some cases, a higher frequency of glitches. If materials are accumulated on the extraction aperture or the extraction electrode 104, the shape of the ion beam 10 extracted from the ion source chamber 202 may be distorted. For example, the shape of the beam 10 may reflect the shape of the materials accumulated on the extraction aperture, the suppression electrode aperture, and/or the ground electrode aperture. Therefore, the ion source may not generate a stable, well-defined ion beam 10. Such a distortion, if excessive, may be difficult to correct with the beam-line components. Accordingly, less than optimal IC may be produced.
One way to prevent the effect of the material accumulation is to intermittently replace the ion source with a clean ion source. Alternatively, the ion source may have to be manually cleaned after powering down the entire ion implanter and after releasing the vacuum. However, these measures require the ion source or the entire ion implanter system 100 to be powered down and to release the vacuum within the system 100. Moreover, the ion implanter system 100, after replacing or cleaning the ion source, must be powered and evacuated to reach operational condition. Accordingly, these maintenance processes may be very time consuming. In addition, the ion implanter system 100 is not used during the maintenance processes. As such, frequent maintenance processes may decrease IC production time, while increasing its manufacturing cost and placing excessive financial burden on the manufacturers and, ultimately, the consumers. In view of the foregoing, it would be desirable to provide a new technique for improving the performance and extending the lifetime of an ion source to overcome the above-described inadequacies and shortcomings.